Oil wells and many other types of wells often comprise a well bore lined with a steel casing. A casing is a string of pipes that are threaded at each end to be interconnected by a series of internally threaded pipe couplings. A lower end of the casing is perforated to allow oil, water, gas, or other targeted fluid to enter the interior of the casing.
Disposed within the casing is another string of pipes interconnected by a series of threaded pipe couplings. This internal string of pipes, known as tubing, has of a much smaller diameter than casing. Fluid in the ground passes through the perforations of the casing to enter an annulus between the inner wall of the casing and the outer wall of the tubing. From there, the fluid forces itself through openings in the tubing and then up through the tubing to ground level, provided the fluid is under sufficient pressure.
If the natural fluid pressure is insufficient, a reciprocating piston pump is installed at the bottom of the tubing to force the fluid up the tubing. A reciprocating drive at ground level is coupled to operate the pump's piston by way of a long string of sucker rods that is driven up and down within the interior of the tubing. A string of sucker rods are typically comprised of individual solid rods that are threaded at each end so they can be interconnected by threaded couplings.
Since casings, tubing and sucker rods often extend thousands of feet, so as to extend the full depth of the well, it is imperative that their respective coupling connections be properly tightened to avoid costly repair and downtime. Couplings for tubulars (i.e., couplings for tubing and casings), and couplings for sucker rods are usually tightened using a tool known as tongs. Tongs vary in design to suit particular purposes, i.e., tightening tubulars or rods, however, each variety of tongs shares a common purpose of torquing one threaded element relative to another. Tongs typically include a hydraulic motor that delivers a torque to a set of jaws that grip the element or elements being tightened.
Various control methods have been developed in an attempt to ensure that sucker rods and tubulars are properly tightened. However, properly tightened joints can be difficult to consistently achieve due to numerous rather uncontrollable factors and widely varying specifications of tubulars and sucker rods. For instance, tubing, casings and sucker rods each serve a different purpose, and so they are each designed with different features having different tightening requirements.
But even within the same family of parts, numerous variations need to be taken into account. With sucker rods, for example, some have tapered threads, and some have straight threads. Some are made of fiberglass, and some are made of stainless steel. Some are a half-inch in diameter, and some are over an inch in diameter. With tubing, some have shoulders, and some do not.
And even for a given part, other conditions may vary. For instance, when tightening the first few sucker rods at the beginning of a day, the hydraulic fluid driving the tongs may be relatively cool and viscous. Later in the day, the hydraulic fluid may warm up, which may cause the tongs to run faster. The hydraulic fluid changing temperature or changing from one set of tongs to another may result in inconsistent tightening of the joints. Even supposedly identical tongs of the same make and model may have different operating characteristics, due to the tongs having varying degrees of wear on their bearings, gears, or seals. Also, the threads of some sucker rods may be more lubricated than others. Some threads may be new, and others may be worn. These are just a few of the many factors that need to be considered when tightening sucker rods and tubulars.
It can be very difficult to provide a control method for tongs that takes into consideration all the various factors that affect the process of tightening tubulars and sucker rods. Since many factors cannot be readily quantified by those who specify the torque to which a particular part should be tightened, specifying a particular torque is risky.
Consequently, a need exists for a display system that adapts to various conditions at a well site where sucker rods, casings, or tubing are being tightened.